1. Field of the Invention
The present invention relates to a p-type electrode structure and a semiconductor light emitting element using the same structure. In detail, the present invention relates to a p-type electrode structure for a wide gap semiconductor and a semiconductor light emitting element using the same structure.
2. Related Art Description
In general, an electrode for a p-type semiconductor is formed of a metal such as Au or Al and is provided as an ohmic electrode by alloying it. In a wide gap semiconductor, it is difficult to obtain an ohmic p-type electrode. In p-type GaN, NiAu is used as an electrode material in order to reduce a resistance thereof. In p-type ZnSe, an electrode structure in which a ZnSe/ZnTe superlattice layer 92 is inserted in between an Au electrode 91 and a p-type ZnSe layer 93 as shown in FIG. 9 is used for a semiconductor laser (cf. Applied Physics Letters, Vol. 61, 1992, pp. 3160-3162) to substantially reduce an operating voltage of the semiconductor laser (cf. Electronics Letters, Vol. 36, 1996, pp. 552).
In a wide gap semiconductor such as the above-mentioned Zn Se or GaN, however, there is a problem that a metal electrode provided on a p-type semiconductor becomes a Schottky type electrode and a resistance of the electrode becomes high. Further, in the electrode structure in which the above-mentioned superlattice is inserted between the metal electrode and the p-type semiconductor layer, there is a problem of reproducibility since a resistance of the electrode is substantially changed by a very small variation of a thickness of the superlattice layer.
There is a further problem that, in the above-mentioned semiconductor laser in which p-type ZnSSe or p-type MgZnSSe is used as a p-type clad layer, a resistance of such wide gap material is high and, thus, an operating voltage of the semiconductor laser becomes high.